linux-kernel - Re: [RFC net-next v3 5/9] net: napi: Add napi

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZuSVBfgrN5wigT90@LQ3V64L9R2.homenet.telecomitalia.it>
Date: Fri, 13 Sep 2024 21:39:49 +0200
From: Joe Damato <jdamato@...tly.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: netdev@...r.kernel.org, mkarsten@...terloo.ca, kuba@...nel.org,
	skhawaja@...gle.com, sdf@...ichev.me, bjorn@...osinc.com,
	amritha.nambiar@...el.com, sridhar.samudrala@...el.com,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>, Jiri Pirko <jiri@...nulli.us>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	David Ahern <dsahern@...nel.org>,
	Johannes Berg <johannes.berg@...el.com>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next v3 5/9] net: napi: Add napi_config

On Fri, Sep 13, 2024 at 10:42:37AM -0700, Stanislav Fomichev wrote:
> On 09/12, Joe Damato wrote:

[...]

> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6493,6 +6493,18 @@ EXPORT_SYMBOL(napi_busy_loop);
> >  
> >  #endif /* CONFIG_NET_RX_BUSY_POLL */
> >  
> > +static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> > +{
> > +	spin_lock(&napi_hash_lock);
> > +
> > +	napi->napi_id = napi_id;
> > +
> > +	hlist_add_head_rcu(&napi->napi_hash_node,
> > +			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> > +
> > +	spin_unlock(&napi_hash_lock);
> > +}
> > +
> >  static void napi_hash_add(struct napi_struct *napi)
> >  {
> >  	if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state))
> > @@ -6505,12 +6517,13 @@ static void napi_hash_add(struct napi_struct *napi)
> >  		if (unlikely(++napi_gen_id < MIN_NAPI_ID))
> >  			napi_gen_id = MIN_NAPI_ID;
> >  	} while (napi_by_id(napi_gen_id));
> 
> [..]
> 
> > -	napi->napi_id = napi_gen_id;
> > -
> > -	hlist_add_head_rcu(&napi->napi_hash_node,
> > -			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> >  
> >  	spin_unlock(&napi_hash_lock);
> > +
> > +	napi_hash_add_with_id(napi, napi_gen_id);
> 
> nit: it is very unlikely that napi_gen_id is gonna wrap around after the
> spin_unlock above, but maybe it's safer to have the following?
> 
> static void __napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> {
> 	napi->napi_id = napi_id;
> 	hlist_add_head_rcu(&napi->napi_hash_node,
> 			   &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> }
> 
> static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> {
> 	spin_lock(&napi_hash_lock);
> 	__napi_hash_add_with_id(...);
> 	spin_unlock(&napi_hash_lock);
> }
> 
> And use __napi_hash_add_with_id here before spin_unlock?

After making this change and re-testing on a couple reboots, I haven't
been able to reproduce the page pool issue I mentioned in the other
email [1].

Not sure if I've just been... "getting lucky" or if this fixed
something that I won't fully grasp until I read the mlx5 source
again.

Will test it a few more times, though.

[1]: https://lore.kernel.org/netdev/ZuMC2fYPPtWggB2w@LQ3V64L9R2.homenet.telecomitalia.it/